The present invention relates to a optical part for two-way optical communications that transmits and receives lightwave signals over a single optical fiber and, more particularly, to an optical part which is disposed opposite either end face of an optical fiber to guide received light from the optical fiber to a light receiving element and launch transmitting light from a light emitting element into the optical fiber end face.
FIG. 16 schematically shows a prior art example of an optical part of this kind, together with an optical fiber, a light emitting element and a light receiving element. In this example the optical part is made up of a prism 11 and two convergent lenses 12 and 13, through which lightwave signals are transmitted and received.
The prism 11 is right triangular in section, and an optical fiber 14 is disposed with its end face opposite a first one 11a of two surfaces of the prism 11 forming therebetween its right angle, and a light receiving element 15 is disposed opposite the second surface 11b of the prism 11 with the lens 12 interposed between them. Outside a third surface 11c of the prism 11, which is its oblique side, there is disposed a light emitting element 16 behind the lens 13.
The light receiving element 15 and the light emitting element 16 are each sealed by transparent resin on a lead frame. In FIG. 16, reference numeral 17 denotes the lead frame and 18 the sealing resin. The light emitting element 16 is such as a laser diode (LD) or light emitting diode (LED), and the light receiving element 15 is, for example, a photodiode (PD).
With such an arrangement as mentioned above, received light 21 exiting from the end face of the optical fiber 14 enters the prism 11 through the surface 11a, then it is reflected by the surface 11c to the side surface 11b and focused through the lens 12 onto the light receiving element 15. On the other hand, transmitting light 22 emitted from the light emitting element 16 is converged by the lens 13, then enters the prism 11 through the surface 11c and travels to the surface 11a, through which it is launched into the end face of the optical fiber 14.
As described above, according to the conventional arrangement shown in FIG. 16, the light path is defined for transmission or reflection, depending on whether the third surface (oblique side) 11c of the prism 11 transmits therethrough or reflects the light incident thereon; in FIG. 16 the hatched portion is shared between transmission and reception.
Accordingly, the prior art suffers from a crosstalk phenomenon that stray light in the prism 11 or the transmitting light 22 is reflected by the first surface (an aperture) 11a of the prism 11 and the end face of the optical fiber 14 to the receiving side as shown in FIG. 17 and impinges on the light receiving element 15. From the viewpoint of performance, the magnitude of crosstalk becomes issue
Further, since the two lenses 12 and 13 are used with a view to providing increased coupling efficiency, the prior art example is large in the component count and hence is expensive, bulky and difficult of miniaturization.